RE: [Jython-users] Singleton [enforce by removing the constructor in the constructor itself]

[O'Brien-Strain, E. <eo...@ex...>]

If you want to enforce the singleton pattern you can remove the constructor
in the constructor itself.  That way only one object can be created.  For
example:

#Define the class
class Foo:
    def __init__(self,...):
        Foo.__init__ = None
        ...
    ...

#Create the one-and-only instance
Foo.instance = Foo(...)


All other code should use "Foo.instance" to refer to the singleton.  If any
other code erroneously tries to create a second Foo it will get a TypeError
complaining about trying to call a non-function.  (For a nicer error
message, instead of assigning __init__ to None you can assign it to a
function that raises a more meaningful exception.)   

__
Eamonn O'Brien-Strain
HP Labs
eo...@hp...




> -----Original Message-----
> From: Ype Kingma [mailto:yk...@xs...]
> Sent: Friday, March 22, 2002 3:27 PM
> To: jyt...@li...
> Subject: Re: [Jython-users] Singleton
> 
> 
> Stephen,
> 
> >Hi,
> >
> >I have read lots of stuff on creating the singleton design 
> pattern using
> >python and to be honest most of this information has left me 
> confused.
> >What is the best way to create the singleton in jython?
> 
> There is no single best way. You can use the borg pattern
> (use google to look for: python borg pattern singleton).
> Or you implement the singleton using module semantics:
> 
> class aSingle: pass
> 
> theSingle = aSingle()
> 
> and use itsModule.theSingle as the singleton.
> 
> Or you can implement it in java as a singleton,
> and access it from from jython.
> 
> There are probably at least a few more other ways.
> 
> >Thanks
> 
> Cheers,
> Ype
> 
> -- 
> 
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